Many techniques for measurement of capacitance are known and have been variously implemented. In many, the voltage levels to which a capacitor which is to be measured is charged and discharged must be precisely determined or there must be accurate determination of the time interval during which measurement is being made. According to one known capacitance measurement technique, a capacitor is charged with a constant current and a time measurement is made from an initial voltage level to a final voltage level, the capacitance being a function of the time interval during which the applied current causes a given voltage change. According to another known technique, a capacitor is charged to some voltage and then discharged into a resistor of known value and the time measured from first voltage level to a second voltage level, the time being proportional to capacitance. Yet another known technique employs a sinusoidal voltage to excite a capacitor and measure the in-phase and quadrature current components from the capacitor, the capacitance being proportional to the ratio of quadrature current to voltage.
According to a further known capacitance measuring technique, described in U.S. Pat. No. 3,480,848, a capacitor is repetitively charged to its fully charged state and discharged to its fully discharged state, the average current measured due to the repetitive discharge of the capacitor being proportional to capacitance. The proportionality of current to capacitance is valid only when the discharge time is sufficient to completely discharge the capacitor.